The growth of semiconductor III-V compounds by chemical vapor deposition (CVD) using organometallics and hydrides as elemental sources has recently developed into a viable process with many potential commercial applications. The metallo-organic chemical vapor deposition (MOCVD) process, based on the pyrolysis of alkyls of group-III elements in an atmosphere of the hydrides of group-V elements, is a common growth technique because it is well adapted to the growth of submicron layers and heterostructures.
Open-tube flow systems are used at atmospheric or reduced pressures in producing the III-V alloys. The process requires only one high-temperature zone for the in situ formation and growth of the semiconductor compound directly on a heated substrate.
Low pressure (LP-) MOCVD growth method offers an improved thickness uniformity and compositional homogeneity, reduction of autodoping, reduction of parasitic decomposition in the gas phase, and allows the growth of high-quality material over a large surface area. Growth by MOCVD takes place far from a thermodynamic equilibrium, and growth rates are determined generally by the arrival rate of material at the growing surface rather than by temperature-dependent reactions between the gas and solid phases.
There have been many III-V materials investigated for long wavelength (8-12 .mu.m) infrared detector applications. So far, InAsSb is the III-V semiconductor alloy with the smallest energy bandgap, but its bandgap is not large enough to cover the entire 8-12 .mu.m range. Even though further reduction in the bandgap has been achieved using strained-layer InAsSb/InSb superlattices, no lattice-matched substrate is available for these materials, so that there remains the problem of obtaining device-quality materials. InTlSb has successfully grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) and a reduction in the bandgap energy of 100 MeV was confirmed through optical characterizations. The lattice of InTlSb was found to contact with increased thallium content and the resulting mismatch with InSb was found to be larger than the predicted estimate. Moreover, a solubility limit of thallium in InSb has been calculated to be .about.15%, beyond which a two-phase region consisting of zinc-blend and CsCl-type structures is predicted. As a result, it is concluded that InTlSb/InSb is inoperative for use in semiconductor applications.